Thermoplastic polymer material for audio and/or optical information recording media

ABSTRACT

The invention concerns moulded discs for audio and/or optical information recording media (such as CDS and DVDs) obtained from a thermoplastic polymer material comprising, by weight, (a) 60 to 95%, preferably 70 to 85%, of a thermoplastic resin selected from (1) a methyl methacrylate homopolymer, (2) a copolymer containing in majority units derived from methyl methacrylate monomer, (3) a mixture of the homopolymer (1) and/or of the copolymer (2) with a substituted or unsubstituted styrene copolymer and of at least one monomer selected from (meth)acrylonitrile, maleic anhydride and maleimides or (4) a glutarimide polymer, optionally mixed with a substituted or unsubstituted styrene/(meth)acrylonitrile copolymer and (b) 5 to 40%, preferably 15 to 30%, of at least one impact modifier compound in the form of particles having an average size of between 10 and 200 nm, preferably between 40 and 150 nm.

This application claims benefit, under U.S.C. §119 or §365 ofFrenchApplication Number 01/14134, filed Oct. 31, 2001; andPCT/FR02/03751 filed Oct. 30, 2002.

FIELD OF THE INVENTION

The invention relates to moulded discs for audio and/or opticalinformation recording media, in particular audio discs (CDs) and DVDs(Digital Versatile Discs or Digital Video Discs), and to a polymerthermoplastic material useful for manufacturing them.

BACKGROUND OF THE INVENTION

Within the context of the invention, the term “thermoplastic polymermaterial” is understood to mean particularly a material based on athermoplastic methacrylic (co)polymer resin, that is to say a methylmethacrylate homopolymer or a copolymer containing predominantly unitsderived from the methyl methacrylate monomer or else resulting fromchemical modification of the methacrylic (co)polymer, for example byimidation.

Methyl methacrylate homopolymers and methacrylic copolymers containingpredominantly methyl methacrylate units are thermoplastic polymersincreasingly used because of their exceptional optical properties (glossand very high transparency, with at least 90% light transmission in thevisible), their ageing resistance, their corrosion resistance and theirresistance to atmospheric agents. Furthermore, these polymers andcopolymers, hereafter called (co)polymers, have a certain advantage formoulded discs useful for manufacturing audio and/or optical informationrecording media because, on the one hand, of their low birefringence(low double refraction index) and, on the other hand, of their high meltflow index which makes it possible, in particular, to obtain discs byconventional injection-moulding techniques or by injection-compressionmoulding, and precise duplication of the “pits” (cavities of smallgeometrical dimensions) of the dies.

These thermoplastic methacrylic (co)polymers, because they are brittle,are liable to break during the various phases of their conversion andduring their transportation and their use. In particular, it has beennoted that moulded discs for audio and/or optical information recordingmedia obtained from these polymers may have cracks that form from thecentre of the discs while they are being manufactured and handled duringthis manufacture and during their use, in particular when packing themin cases.

It is known to add impact modifier compounds in order to improve theimpact strength of these methacrylic (co)polymers. However, although thecrack resistance is considerably improved, the results are still notsatisfactory since it is no longer possible to obtain correctduplication of the pits.

In the present invention, the aim is therefore to seekthermoplastic-polymer-based materials that allow the manufacture ofmoulded discs for audio and/or optical information recording media thatare crack-resistant, while preserving the properties necessary for thistype of product, especially the ability of correctly duplicating thepits, without forgetting transparency and birefringence.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention firstly to providemoulded discs for audio and/or optical information recording media,obtained from a thermoplastic polymer material comprising, by weight:

(a) 60 to 95%, preferably 70 to 85%, of a thermoplastic resin chosenfrom:

-   -   (1) a methyl methacrylate homopolymer,    -   (2) a copolymer containing predominantly units derived from the        methyl methacrylate monomer,    -   (3) a blend of the homopolymer (1) and/or of the copolymer (2)        with a copolymer of a substituted or unsubstituted styrene with        at least one monomer chosen from (meth)acrylonitrile, maleic        anhydride and maleimides or    -   (4) a glutarimide polymer, optionally blended with a substituted        or unsubstituted styrene/(meth)acrylonitrile copolymer; and

(b) 5 to 40%, preferably 15 to 30%, of at least one impact modifiercompound in the form of particles having an average size of between 10and 200 nm, preferably between 40 and 150 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a test piece, produced from thethermoplastic polymer material, to be subjected to a tensile testaccording to Test 1 described below measuring the crack resistance ofthe said test piece. In this diagram, the test piece is shown in theform of a rectangle of width “L”. Midway along the test piece there aretwo notches “a”. The distance between the ends of these two notches isequal to L−2a and corresponds to the length of the “ligament” to bebroken.

FIG. 2 is a diagram of a set-up for measuring the crack resistance of adisc according to Test 2 described below. Shown in this diagram are adisc (1) whose crack resistance it is desired to measure, a punch (2)provided with two fins (3) making an angle of 30° with the verticaldirection of the punch, this punch having an end in the form of a ball(4) with a diameter of 14 mm. This punch is placed near the centre ofthe disc for the purpose of its impacting this part of the disc.

FIGS. 3 to 5 show a view using atomic force microscopy of thereplication of pits on DVD discs obtained in Examples 1 and 2 (controls)and Example 3 (according to the invention).

DETAILED DESCRIPTION OF THE INVENTION

The thermoplastic resin (a) may be formed from methyl methacrylatehomopolymer (1) and/or from a copolymer (2) containing predominantlyunits derived from the methyl methacrylate monomer. These (co)polymers(1) and (2) comprise from 51 to 100%, preferably from 80 to 99%, byweight of methyl methacrylate units and from 0 to 49%, preferably 1 to20%, by weight of units derived from monoethylenically unsaturatedcomonomers copolymerizable with methyl methacrylate.

To form the copolymer (2), the methyl methacrylate monomer may bepolymerized with one or more comonomers. The monoethylenicallyunsaturated comonomer(s) copolymerizable with the methyl methacrylatemonomer is (are) especially chosen from acrylic, methacrylic, maleimide,maleic anhydride and styrene monomers.

As acrylic monomers, mention may be made of alkyl acrylates in which thealkyl group has from 1 to 10 carbon atoms (such as methyl acrylate,ethyl acrylate and n-butyl, 2-ethylhexyl and isobutyl acrylate),hydroxyalkyl or alkoxyalkyl acrylates, in which the alkyl group has from1 to 4 carbon atoms, acrylamide and acrylonitrile.

As methacrylic monomers, mention may be made of alkyl methacrylates inwhich the alkyl group has from 2 to 10 carbon atoms (such as ethyl,isobutyl, secondary butyl and tertiary butyl methacrylate), isobornylmethacrylate, methacrylonitrile and hydroxyalkyl or alkoxyalkylmethacrylates in which the alkyl group has from 1 to 4 carbon atoms.

As maleimide monomers, mention may be made of N-cyclohexylmaleimide andN-isopropylmaleimide.

The thermoplastic resin (9) may also be formed from a blend (3)comprising, by weight, 60 to 97%, preferably 70 to 95%, of a methylmethacrylate homopolymer (1) and/or of a copolymer (2) containingpredominantly units derived from the methyl methacrylate monomer, and 3to 40%, preferably 5 to 30%, of a substituted or unsubstitutedstyrene/(meth)acrylonitrile copolymer and/or of a substituted orunsubstituted styrene/maleic anhydride copolymer (SMA) and/or of asubstituted or unsubstituted styrene/maleimide copolymer.

The substituted or unsubstituted styrene/(meth)acrylonitrile copolymeris advantageously formed, by weight, from 8 to 35% of(meth)acrylonitrile and from 65 to 92% of substituted or unsubstitutedstyrene.

The substituted or unsubstituted styrene/maleic anhydride copolymer(SMA) is advantageously formed, by weight, from 8 to 33% of maleicanhydride and from 67 to 92% of substituted or unsubstituted styrene.

The substituted or unsubstituted styrene/maleimide copolymer, that canbe used in the invention, is advantageously formed, by weight, from 8 to21% of maleimides and from 72 to 92% of substituted or unsubstitutedstryene. As maleimides, mention may be made of N-cyclohexylmaleimide andN-isopropylmaleimide.

As substituted styrene for these copolymers, it is possible to usealpha-methylstyrene, monochlorostyrene and tert-butylstyrene monomers.

The thermoplastic resin (9) may also consist of a glutarimide polymer(4) comprising imide units of formula:

in which the symbols R₁, R₂ and R₃ are identical or different and may behydrogen or a substituted or unsubstituted alkyl, aryl, alkaryl oraralkyl group having from 1 to 20 carbon atoms. The substituents may bechosen from halogen atoms and methyl, ethyl, hydroxyl, methoxy, ethoxy,carboxyl and ethylcarbonyl groups. The degree of imidation is at least40%.

These glutarimide polymers that can be used in the invention aredescribed, for example, in patent U.S. Pat. No. 4,954,574 and thedocument EP-A-515 095.

It is also possible to use, as thermoplastic resin (a), a polymer blend,like that described in the document EP-A-515 095, which comprises acopolymer having glutarimide groups and a styrene or substitutedstyrene/(meth)acrylonitrile copolymer. The blend may comprise, byweight, from 40 to 85% of glutarimide polymer, and from 15 to 60% of(meth)acrylonitrile.

It is advantageous to use, as thermoplastic resin (a), a copolymer (2)containing predominantly units derived from the methyl methacrylatemonomer. Particularly advantageous is a methyl methacrylate/alkylacrylate copolymer in which the alkyl group has from 1 to 4 carbonatoms, the amount of alkyl acrylate representing up to 6%, preferablyfrom 0.5 to 5%, and more particularly from 0.1 to 3%, by weight of thepolymer. Such copolymers are described in the documents WO 98/57799 andWO 99/65671.

The thermoplastic resin (a) generally has a weight-average molecularmass (M_(w)), measured by steric exclusion chromotography using methylmethacrylate homopolymer standards for the calibration, of between50,000 and 200,000 g/mol, preferably between 60,000 and 140,000 g/mol.

In accordance with the invention, the thermoplastic polymer materialused to manufacture the moulded discs for audio and/or opticalinformation recording media furthermore includes at least one impactmodifier compound (also called impact modifier) whose average size isbetween 10 and 200 nm, preferably between 40 and 150 nm and inparticular between 80 and 120 nm.

These “impact modifiers” are products based on elastomeric materials.These impact modifiers are generally polymer substances having amultilayer structure, at least one of the layers consisting of anelastomer phase. Given that it is the elastomer phase contained in theadditive that gives the impact strength, this additive is added to thebrittle thermoplastic in order to have a suitable proportion of theelastomer.

The impact modifier compound useful within the invention may consist ofa block copolymer comprising at least one elastomer block resulting fromthe polymerization of monomers such as butadiene, substituted orotherwise, alkyl acrylates or aralkyl acrylates. This may in particularbe a diblock copolymer such as poly(butadiene-block-methyl methacrylate)or a triblock copolymer such aspoly(styrene-block-butadiene-block-methyl methacrylate), in whichcopolymers the polybutadiene elastomer phase represents up to about 50%by weight of the mass of the block copolymer. The butadiene block may beunhydrogenated, partially hydrogenated or completely hydrogenated. Thismay also be a poly(methyl methacrylate-block-butyl acrylate-block-methylmethacrylate), copolyether esteramides having polyamide and polyetherblocks, and copolymers having polyester and polyether blocks.

The impact modifier compound may also be a polymer substance having amultilayer structure, at least one of the layers consisting of anelastomer phase. These polymer substances may thus be particles obtainedby coagulation, drying, spraying or atomization of an elastomer latex.The manufacture of such latices, used for increasing the impact strengthof thermoplastic matrices, is well known to those skilled in the art. Inparticular, it is known that by modifying the conditions under whichthese latices are manufactured, it is possible to vary their morphologyand consequently their ability to improve the impact strength and theirability to maintain the optical properties of the matrix to bereinforced.

The various elastomer latex morphologies known at the present time willbe able to be used without any problem within the context of the presentinvention. In particular, it will be possible to use a latex with a“soft-hard” morphology, the first phase (or core) of which is anelastomer and the “hard” final phase (or external layer) of which is abrittle thermoplastic. These latices may be obtained in two steps, forexample, in a first step, by the emulsion polymerization, in an aqueousmedium in the presence of an initiator generating free radicals and ofan emulsifier, of at least one monomer (called a “soft” monomer, that isto say a monomer resulting in a polymer having a glass transitiontemperature below 25° C.) that has to constitute the elastomer phase,chosen for example from monomers such as butadiene, substituted orotherwise, and alkyl or aralkyl acrylates in which the alkyl group hasfrom 1 to 15 carbon atoms and, in a second step, by again the emulsionpolymerization, in the presence of the polymer of the first step, of atleast one monomer that has to constitute a “hard” phase compatible withthe brittle thermoplastic polymer (the matrix) of which it is desired toimprove the impact strength. This or these monomers (called “hard”monomers, that is to say monomers resulting in a polymer having a glasstransition temperature greater than or equal to 25° C.) may be chosen,for example, from alkyl methacrylates in which the alkyl group containsfrom 1 to 4 carbon atoms, vinylaromatic monomers such as styrene andsubstituted styrenes, and acrylonitrile and methacrylonitrile monomers.The “hard” phase may also be obtained from a mixture of the above hardmonomers (in a predominant amount) and of one or more ethylenicallyunsaturated comonomers, such as a lower alkyl acrylate or (meth)acrylicacid.

Optionally, the polymerization of the monomers not constituting the“hard” final phase may be carried out in the presence of otherethylenically unsaturated polyfunctional monomers copolymerizable withthe former monomers, particularly crosslinking and/or grafting monomers.The polymer constituting the final “hard” phase may be formed in thepresence of a crosslinking monomer. As well-known crosslinking monomersthat can be used, mention may be made of polyol polyacrylates andpolymethacrylates, such as alkylene glycol diacrylates anddimethacrylates; as grafting monomers that can be used, mention may bemade of allyl esters, such as allyl acrylate and methacrylate.

Thus, as disclosed in FR-A-2 092 389, the elastomer phase may beprepared from a mixture comprising, by weight, at least 50% of an alkylor aralkyl acrylate, in which the alkyl group has from 1 to 15 carbonatoms, 0.05 to 5.0% of a crosslinking monomer, 0.05 to 5% of graftingmonomers and 0 to 10% of a hydrophilic monomer (such as (meth)acrylicacid, hydroxylated alkyl esters of methacrylic acid and amides), thebalance optionally consisting of other ethylenically unsaturatedcopolymerizable monomers (such as styrene); the final brittlethermoplastic phase, polymerized in the presence of the elastomer phase,may be obtained from a monomer mixture comprising at least 50% by weightof an alkyl methacrylate, the elastomer phase and the thermoplasticphase having a minimum degree of chemical attachment of about 20%.

It will also be possible to use a latex with a “hard-soft-hard”morphology, the non-elastomer first phase (or core) of which ispolymerized from the monomers that may form the methacrylic (co)polymermaterial to be reinforced (a) or the abovementioned “hard” final phase,the intermediate phase of which is an elastomer obtained, for example,from the abovementioned so-called “soft” monomers and the final phase ofwhich is formed from monomers that can be used for the methacrylic(co)polymer material (a) or the abovementioned “hard” final phase.Particularly suitable is a latex like that described in U.S. Pat. No.3,793,402, which latex is formed (1) from a non-elastomer coreconsisting of a copolymer obtained from 80 to 100% by weight of at leastone so-called “hard” monomer, such as an alkyl methacrylate (the alkylbeing C₁-C₄), styrene, (meth)acrylonitrile optionally combined (at 0-30%by weight) with one or more ethylenically unsaturated comonomers, suchas a lower alkyl (meth)acrylate (the alkyl being C₁-C₄) and(meth)acrylic acid, 0 to 10% by weight of a polyfunctional crosslinkingmonomer and 0 to 10% by weight of a grafting monomer, such as thosementioned above, (2) from an elastomer intermediate layer, formed in thepresence of the polymer (1) from 50 to 99.9% by weight of one or morebutadiene monomers, substituted or otherwise, and/or an alkyl acrylatein which the alkyl group has from 1 to 8 carbon atoms, from 0 to 49.9%by weight of one or more ethylenically unsaturated comonomers, such aslower alkyl (meth)acrylates (the alkyl being C₁-C₄), (meth)acrylic acidand styrene, from 0 to 5% by weight of a polyfunctional crosslinkingmonomer and from 0.05 to 5% by weight of a grafting monomer, such asthose mentioned above and (3) from a so-called “hard” or compatibilizingexternal layer formed, in the presence of the polymers (1) and (2), from“hard” monomers (C₁-C₄ alkyl methacrylate, styrene or(meth)acrylonitrile) optionally combined (at 0-30% by weight) withethylenically unsaturated comonomers, such as a lower alkyl(meth)acrylate (the alkyl being C₁-C₄). In particular, the variousphases—core (1), intermediate layer (2) and external layer(3)—represent, respectively, 10 to 40%, 20 to 60% and 10 to 70% byweight of the total mass of the trilayer (or triphase) compositecopolymer.

It is also possible to use a product with a soft/hard/soft/hardmorphology, as disclosed in the document EP-B-270865, which comprises(1) a central core based on a crosslinked elastomer intimately blendedwith a thermoplastic methacrylic (co)polymer resin, (2) an optionalfirst layer of the said resin grafted onto the central core, (3) asecond layer of crosslinked elastomer grafted onto the said first layeror onto the said core and (4) a third resin layer grafted onto the saidcrosslinked elastomer second layer.

Other morphologies that could be used are those more complex onesdisclosed in the patents U.S. Pat. No. 4,052,525 and FR-A-2 446 296.

The impact modifier compound (b) used in the invention is advantageouslyin the form of a multilayer composite copolymer.

The thermoplastic polymer material may optionally contain standardadditives, such as lubricants and UV stabilizers, in an amount from 0%to 1% by weight in relation to the total weight of the material.

The thermoplastic polymer material is advantageously in the form ofgranules allowing moulded discs according to the invention to bemanufactured by injection moulding or injection-compression moulding.

The thermoplastic resin (a), when it is formed by a methacrylic(co)polymer, may be obtained by any known process, for example bysuspension or mass polymerization. It may be in the form of granules orbeads. The beads are obtained by the well-known process of aqueoussuspension polymerization of one or more monomers in the presence of aninitiator soluble in the monomer(s) and of a suspension agent. Thegranules may be obtained from these beads, which are melted in anextruder to form rods; the latter are then cut into granules. Thegranules may also be prepared by mass polymerization, a well-knownprocess, consisting in polymerizing the monomer(s) or else a prepolymersyrup dissolved in the monomer(s) in the presence of an initiator. Thepolymer obtained is forced, at the end of the line, through a die inorder to obtain rods, that are then cut into granules. For thepreparation of beads and granules, it is also possible to add a chaintransfer agent to control the molar mass of the polymer, and optionallyother useful additives.

The thermoplastic polymer material used according to the invention maybe obtained by melt-blending the granules and/or beads of thermoplasticresin (a), particularly methacrylic (co)polymers, of at least one impactmodifier compound (b), usually in powder form, and optionally of otheradditives, such as lubricants and UV stabilizers. This blend may beproduced in any suitable device, for example an extruder, generally at atemperature of around 220° C. The blend is then in the form of granules,which can be used to manufacture discs moulded by injection-compressionmoulding.

The moulded discs according to the invention may be obtained by anyknown process, and in particular by injection moulding orinjection-compression moulding of the granules in an injection-mouldingmachine at a temperature of at least 250° C., as described inApplication WO 98/57799.

It is also an object of the present invention to provide moulded discssuitable as audio and/or optical information recording media (such asDVDs), comprising at least one moulded disc as described above.

DVD discs are typically obtained by joining together, by means of anadhesive, a first moulded disc metallized by sputtering and a second,optionally metallized, moulded disc.

It is also an object of the present invention to provide a novelthermoplastic polymer material that is useful in particular for themanufacture of moulded discs for information recording media, the saidmaterial being as defined above, and furthermore characterized in thatit comprises, by weight:

(a) from 70 to 85% of a thermoplastic resin chosen from:

-   -   (1) a methyl methacrylate homopolymer,    -   (2) a methyl methacrylate/alkyl acrylate copolymer in which the        alkyl group has from 1 to 4 carbon atoms, the amount of alkyl        acrylate representing from 0.1 to 3% of the copolymer,    -   (3) a blend of the homopolymer (1) and/or of the copolymer (2)        with a copolymer of a substituted or unsubstituted styrene with        at least one monomer chosen from (meth)acrylonitrile, maleic        anhydride and maleimides or    -   (4) a glutarimide polymer, optionally blended with a substituted        or unsubstituted styrene/(meth)acrylonitrile copolymer; and

(b) from 15 to 30% of at least one impact modifier compound in the formof particles having an average size of between 10 and 200 nm, preferablybetween 40 and 150 nm.

The following examples illustrate the invention.

EXAMPLES

The crack resistance was determined by the following tests:

1. Test on the test pieces (Test 1):

Granules of thermoplastic polymer material obtained by melt-blendingthermoplastic resin granules (a) with an impact modifier (b) were heatedin an oven for 4 h at 70° C. They were then extruded in the form of astrip using a FAIREX-type single-screw extruder, with no venting ports,fitted with an appropriate flat die. The strips, 35 mm in width and 0.6mm in thickness (E), were then cooled by a non-thermostatted calender.

Specimens 90 mm in length were taken from the various strips produced(the dimensions of each specimen were 90 mm×35 mm×0.6 mm). Test piecesfor undergoing a tensile test were thus prepared, as in FIG. 1, with alength of 90 mm and a width “L” of 35 mm, the thickness (E) being 0.6mm.

Notching:

The notch the test piece, two tapered notches “a” facing each other (seeFIG. 1) were machined at mid-length of the test piece. The crack length“a” of the test pieces, ready to be tested, must lie within the limitsgiven by 0.45 L/2≦a≦0.55 L/2. The distance (L−2a) represents the lengthof the “ligament” to be broken.

Next, a natural crack is produced by pressing lightly on a fresh razorblade in the notches by means of a micrometer screw. The increase inlength of the crack thus obtained (0.1 mm) was more than four times theoriginal radius of the tip of the notch.

Conditioning:

The test piece was then conditioned for 24 hours (at 23° C. and 50%relative humidity).

Test machine and set-up:

The mechanical tests were carried out on a ADHAMEL DY30 test machinefrom MTS. During the tensile test, the test piece was held by means oftwo clamping jaws.

Test conditions:

The tests were carried out at 23° C. and at a test speed of 10 mm/min. Aminimum of five tests were carried out on each material.

Determination of the crack resistance:

The fracture toughness (or toughness) G was calculated using thefollowing equation, that is to say from the work W (performed until themoment when the crack propagates in the absence of additional stress)divided by the surface area of the broken ligament:

-   -   G=W/(E(L−2a)) expressed in kJ/m²        where:    -   W is the work performed (the area under the force-displacement        curve);    -   E is the thickness of the test piece; and    -   (L−2a) is the length of the broken ligament.

2) Test on DVD discs (Test 2)

The crack resistance, measured on the DVD discs, was measured using anMTS 831 test machine from MTS according to the principle shown in FIG.2.

Test machine and set-up:

In the cracking test, the disc (1), with a diameter of 108 mm, was heldbetween four diametrically opposed bearing points (not shown in thediagram) and was stressed at its centre by means of the punch (2).

Test conditions:

The tests were carried out at 23° C. and at a test speed of 10 mm/min. Aminimum of five tests were carried out on each material.

Determination of the crack resistance:

The crack resistance was calculated from the work W performed to themoment when a crack propagates, in the absence of additional stress,from the centre of the disc. W, expressed in mJ, represents the workperformed (the area under the force-displacement curve).

EXAMPLE 1 Control

Granules of the methyl methacrylate (97 wt %)/ethyl acrylate (3 wt %)copolymer having a weight-average molar mass of 75,000 g/mol were used.These granules were extruded as a strip 35 mm in width and 0.6 mm inthickness using a FAIREX-type single-screw extruder fitted with asuitable flat die. Specimens 90 mm in length were taken from the strip.The refractive index was 1.49.

The fracture toughness (G) was determined according to theabovementioned Test 1 cracking test. It was 1.71±0.26 kJ/m².

Next, these granules were injection-moulded on a video disc (DVD)manufacturing line from Singulus. The thickness of the DVD was 1.2 mm.The crack resistance, measured after Test 2 (DVD crack resistance test),was 14 mJ±3. Replication of the pits was checked by atomic forcemicroscopy. The replication was excellent (see FIG. 3).

EXAMPLE 2 Control

77 parts by weight of granules of a methyl methacrylate/ethyl acrylate(97/3 wt %) copolymer having a weight-average molar mass of 75,000 g/moland 23 parts by weight of the impact modifier in powder form given belowwere extrusion-blended at a temperature of about 220° C. in an 11D Bussco-kneader fitted with a weigh feeder.

This impact modifier was in the form of three-layer granules having thecomposition described in Example 2 of U.S. Pat. No. 3,793,402, that isto say:

-   -   a core formed from a methyl methacrylate (99.8%)/allyl        methacrylate (0.2%) copolymer;    -   an interlayer formed from a butyl acrylate (79.4%)/styrene        (18.6%)/allyl methacrylate (0.2%) copolymer; and    -   an outer layer formed from a methyl methacrylate (96%)/ethyl        acrylate (4%) copolymer;        the distribution, by weight, from the core, of the interlayer        and the outer layer being 30%, 50% and 20% respectively.

The average size of the impact modifier powder particles was 300 nm. Therefractive index was 1.49.

The granules obtained were extruded as a strip as in Example.

The fracture toughness G was determined according to the abovementionedTest 1 cracking test. It was 20.13±4.35 kJ/m².

Next, these granules were injection-moulded on a video disc (DVD)manufacturing line from Singulus. The thickness of the DVD was 1.2 mm.The crack resistance, measured after. Test 2 (DVD crack resistance), was108 mJ±15. Replication of the pits was checked by atomic forcemicroscopy. Replication was very bad (see FIG. 4).

EXAMPLE 3 According to the Invention

80 parts by weight of granules of a methyl methacrylate/ethyl acrylate(97/3 wt %) copolymer having a weight-average molar mass of 75,000 g/moland 20 parts by weight of the impact modifier in powder form wereextruder-blended at a temperature of about 220° C. in an 11D Bussco-kneader fitted with a weigh feeder.

The impact modifier was a two-layer compound: soft core (70 wt %)/hardshell (30 wt %) in which the core consisted of a butyl acrylate (48 wt%)/butadiene (52 wt %) copolymer and the shell consisted of a methylmethacrylate (96 wt %)/ethyl acrylate (4 wt %) copolymer. The averagesize was 100 nm. The refractive index was 1.49.

The granules obtained were extruded as a strip as in Example 1.

The fracture toughness G was determined according to the abovementionedTest 1 cracking test. It was 57.10±6.48 kJ/m².

Next, these granules were injection-moulded on a video disc (DVD)manufacturing line from Singulus. The thickness of the DVD was 1.2 mm.The crack resistance, measured after Test 2 (DVD crack resistance), was945 mJ±140. Replication of the pits was checked by atomic forcemicroscopy. Replication was excellent (see FIG. 5).

1-17. cancel
 18. Moulded discs for audio and/or optical informationrecording media, obtained from a thermoplastic polymer materialcomprising, by weight: (a) 60 to 95%. of a thermoplastic resin chosenfrom: (1) a methyl methacrylate homopolymer, (2) a copolymer containingpredominantly units derived from the methyl methacrylate monomer, (3) ablend of the homopolymer (1) and/or of the copolymer (2) with acopolymer of a substituted or unsubstituted styrene with at least onemonomer chosen from (meth)acrylonitrile, maleic anhydride and maleimidesor (4) a glutarimide polymer, optionally blended with a substituted orunsubstituted styrene/(meth)acrylonitrile copolymer; and (b) 5 to 40%,of at least one impact modifier compound in the form of particles havingan average size of between 10 and 200 nm, preferably between 40 and 150nm.
 19. Moulded discs according to claim 18 comprising by weight 70 to85% of said thermoplastic resin.
 20. Moulded discs according to claim 18comprising by weight 15 to 30%, of at least one impact modifier compoundin the form of particles.
 21. Moulded discs according to claim 18,characterized in that the copolymer (2) containing predominantly unitsderived from the methyl methacrylate monomer is formed from 51 to 100%,by weight of methyl methacrylate units and from 0 to 49%, by weight ofunits derived from monoethylenically unsaturated comonomerscopolymerizable with methyl methacrylate.
 22. Moulded discs according toclaim 21 characterized in that the copolymer (2) containingpredominantly units derived from the methyl methacrylate monomer isformed from 80 to 99%, by weight of methyl methacrylate units and from 1to 20%, by weight of units derived from monoethylenically unsaturatedcomonomers copolymerizable with methyl methacrylate.
 23. Moulded discsaccording to claim 21, characterized in that the monoethylenicallyunsaturated comonomer or comonomers is/are chosen from acrylic,methacrylic, maleimide, maleic anhydride and styrene monomers. 24.Moulded discs according to claim 18, characterized in that thethermoplastic resin (a) is a blend (3) comprising, by weight, 60 to 97%,of a methyl methacrylate homopolymer (1) and/or of a copolymer (2)containing predominantly units derived from the methyl methacrylatemonomer, and 3 to 40%, of a substituted or unsubstitutedstyrene/(meth)acrylonitrile copolymer and/or of a substituted orunsubstituted styrene/maleic anhydride copolymer (SMA) and/or of asubstituted or unsubstituted styrene/maleimide copolymer.
 25. Mouldeddiscs according to claim 24, characterized in that the thermoplasticresin (a) is a blend (3) comprising, by weight, 70 to 95%, of a methylmethacrylate homopolymer (1) and/or of a copolymer (2) containingpredominantly units derived from the methyl methacrylate monomer, and 5to 30%, of a substituted or unsubstituted styrene/(meth)acrylonitrilecopolymer and/or of a substituted or unsubstituted styrene/maleicanhydride copolymer (SMA) and/or of a substituted or unsubstitutedstyrene/maleimide copolymer.
 26. Moulded discs according to claim 24,characterized in that the substituted or unsubstitutedstyrene/(meth)acrylonitrile copolymer is formed, by weight, from 8 to35% of (meth)acrylonitrile and from 65 to 92% of substituted orunsubstituted styrene.
 27. Moulded discs according to claim 24,characterized in that the substituted or unsubstituted styrene/maleicanhydride copolymer (SMA) is formed, by weight, from 8 to 33% of maleicanhydride and from 67 to 92% of substituted or unsubstituted styrene.28. Moulded discs according to claim 24, characterized in that thesubstituted or unsubstituted styrene/maleimide copolymer is formed, byweight, from 8 to 21% of maleimides and from 79 to 92% of substituted orunsubstituted styrene.
 29. Moulded discs according to claim 18,characterized in that the thermoplastic resin (a) is a glutarimidepolymer (4) comprising imide units of formula:

in which the symbols R₁, R₂ and R₃ are identical or different and may behydrogen or a substituted or unsubstituted alkyl, aryl, alkaryl oraralkyl group having from 1 to 20 carbon atoms, the degree of imidationbeing at least 40%.
 30. Moulded discs according to claim 18,characterized in that the impact modifier compound (b) is a blockcopolymer comprising at least one elastomer block or a multilayercomposite copolymer comprising at least one elastomer layer.
 31. Mouldeddiscs according to claim 30, characterized in that the elastomer blockof the block copolymer consists of a polymer derived from butadiene,substituted or otherwise, alkyl acrylate or aralkyl acrylate monomers.32. Moulded discs according to claim 30, characterized in that theelastomer layer of the multilayer composite copolymer is formed by apolymer derived from butadiene, substituted or otherwise, alkyl acrylateor aralkyl acrylate monomers, optionally monoethylenically unsaturatedcomonomers, or crosslinking and/or grafting monomers.
 33. Moulded discsaccording to claim 18, characterized in that the thermoplastic polymermaterial is in the form of granules.
 34. Moulded discs according toclaim 18, characterized in that said moulded discs are obtained by theinjection moulding or injection-compression moulding of thethermoplastic polymer material.
 35. Moulded discs according to claim 18comprising at least one moulded disc.
 36. Moulded discs according toclaim 35, obtained by joining together, by means of an adhesive, twomoulded discs, at least one of the moulded discs being metallized. 37.Thermoplastic polymer material characterized in that it comprises, byweight: (a) from 70 to 85% of a thermoplastic resin chosen from: (1) amethyl methacrylate homopolymer, (2) a methyl methacrylate/alkylacrylate copolymer in which the alkyl group has from 1 to 4 carbonatoms, the amount of alkyl acrylate representing from 0.1 to 3% of thecopolymer, (3) a blend of the homopolymer (1) and/or of the copolymer(2) with a copolymer of a substituted or unsubstituted styrene with atleast one monomer chosen from (meth)acrylonitrile, maleic anhydride andmaleimides or (4) a glutarimide polymer, optionally blended with asubstituted or unsubstituted styrene/(meth)acrylonitrile copolymer; and(b) from 15 to 30% of at least one impact modifier compound in the formof particles having an average size of between 10 and 200 nm, preferablybetween 40 and 150 nm.
 38. Process for manufacturing the thermoplasticpolymer material according to claim 18 or 37, in the form of granules bymelt-blending at least the thermoplastic polymer resin (a) and theimpact modifier compound (b).